35,111 research outputs found

    Improving Automatic Content Type Identification from a Data Set

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    Data file layout inference refers to building the structure and determining the metadata of a text file. The text files dealt within this research are personal information records that have a consistent structure. Traditionally, if the layout structure of a text file is unknown, the human user must undergo manual labor of identifying the metadata. This is inefficient and prone to error. Content-based oracles are the current state-of-the-art automation technology that attempts to solve the layout inference problem by using databases of known metadata. This paper builds upon the information and documentation of the content-based oracles, and improves the databases of the oracles through experimentation

    Gamma-Ray Burst Afterglows: Effects of Radiative Corrections and Nonuniformity of the Surrounding Medium

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    The afterglow of a gamma-ray burst (GRB) is commonly thought to be due to continuous deceleration of a relativistically expanding fireball in the surrounding medium. Assuming that the expansion of the fireball is adiabatic and that the density of the medium is a power-law function of shock radius, viz., nextRkn_{ext}\propto R^{-k}, we analytically study the effects of the first-order radiative correction and the nonuniformity of the medium on a GRB afterglow. We first derive a new relation among the observed time, the shock radius and the fireball's Lorentz factor: t=R/4(4k)γ2ct_\oplus=R/4(4-k)\gamma^2c, and also derive a new relation among the comoving time, the shock radius and the fireball's Lorentz factor: tco=2R/(5k)γct_{co}=2R/(5-k)\gamma c. We next study the evolution of the fireball by using the analytic solution of Blandford and McKee (1976). The radiation losses may not significantly influence this evolution. We further derive new scaling laws both between the X-ray flux and observed time and between the optical flux and observed time. We use these scaling laws to discuss the afterglows of GRB 970228 and GRB 970616, and find that if the spectral index of the electron distribution is p=2.5p=2.5, implied from the spectra of GRBs, the X-ray afterglow of GRB970616 is well fitted by assuming k=2k=2.Comment: 17 pages, no figures, Latex file, MNRAS in pres

    Temporal variability in early afterglows of short gamma-ray bursts

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    The shock model has successfully explained the observed behaviors of afterglows from long gamma-ray bursts (GRBs). Here we use it to investigate the so-called early afterglows from short GRBs, which arises from blast waves that are not decelerated considerably by their surrounding medium. We consider a nearby medium loaded with e±e^{\pm} pairs (Beloborodov 2002). The temporal behaviors show first a soft-to-hard spectral evolution, from the optical to hard X-ray, and then a usual hard-to-soft evolution after the blast waves begin to decelerate. The light curves show variability, and consist of two peaks. The first peak, due to the pair effect, can be observed in the X-ray, though too faint and too short in the optical. The second peak will be easily detected by {\it Swift}. We show that detections of the double-peak structure in the light curves of early afterglows are very helpful to determine all the shock parameters of short GRBs, including both the parameters of the relativistic source and the surroundings. Besides, from the requirement that the forward-shock emission in short GRBs should be below the BATSE detection threshold, we give a strong constraint on the shock model parameters. In particular, the initial Lorentz factor of the source is limited to be no more than 103\sim 10^3, and the ambient medium density is inferred to be low, n\la 10^{-1} cm3^{-3}.Comment: 5 pages, 1 figure, minor changes to match the publish in MNRA

    A Generic Dynamical Model of Gamma-ray Burst Remnants

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    The conventional generic model is deemed to explain the dynamics of γ\gamma-ray burst remnants very well, no matter whether they are adiabatic or highly radiative. However, we find that for adiabatic expansion, the model could not reproduce the Sedov solution in the non-relativistic phase, thus the model needs to be revised. In the present paper, a new differential equation is derived. The generic model based on this equation has been shown to be correct for both radiative and adiabatic fireballs, and in both ultra-relativistic and non-relativistic phase.Comment: 10 pages, LaTeX, 4 postscript figures, accepted for publication in MNRA